This invention relates generally to improvements in transmissions for the drawworks of drilling rigs.
More specifically, but not by way of limitation, this invention relates to an improved shifting apparatus for a drawworks transmission wherein the transmission includes at least a high, low and neutral position, and wherein the transmission is locked in each of the positions.
As oilwell drilling rigs have developed over the last several years, they have become much larger and have become dispersed over a relatively large area. In the case of portable rigs, for example, rigs that have been developed for helicopter transport, various rig components are totally separate and even when assembled remain fairly widely dispersed. The drawworks, that is the hoisting apparatus utilized to move the pipe into and out of the well, is located generally on the rig floor while the engines for driving the drawworks may be located at some remote lccation.
U.S. Pat. No. 2,704,653, issued Mar. 22, 1955 to D. M. Duncan illustrates a rotary and drawworks drive system utilized in one type of drilling rig. U.S. Pat. No. 3,981,485 issued Sept. 21, 1976 to K. H. Eddy et al illustrates a helicopter portable drilling rig and the drive system utilized therein.
The number of engines utilized to drive the turntable and the drawworks, has been increasing over the years so that now, many engines are compounded to provide the desired horsepower. Further, the operator of the rig can not be located close to all the rig apparatus. Accordingly, to be able to control the engines and the transmissions linking the engines with apparatus on the drilling rig floor from a remote location, it has become necessary to provide controls for the rig components that can be operated from remote locations.
Remote mechanical shifting of the drawworks transmission, engagement and disengagement of clutches and brakes for the engines and the drawworks, has been accomplished through the extensive use of flexible cables and other mechanical linkages. In such instances, extreme distances become very difficult and even in relatively close proximity installations, a great deal of care must be utilized to be certain that the cables are not placed in a position that would hamper the operation thereof.
Hydraulic mechanisms have also been utilized to control the clutches and brakes and to shift the transmissions. However, such hydraulic installations necessitate the use of a special hydraulic pump and some means for driving the pump which requires additional equipment, expense and maintenance.
Drilling rigs are almost always equipped with compressors so that a source of pressurized air is readily available.